The quick table
- 10 MB over 30 seconds: about 2.7 Mbps. Plenty for a clean 1080p clip.
- 10 MB over 2 minutes: about 0.7 Mbps. Fine at 720p, soft at 1080p.
- 20 MB over 2 minutes: about 1.3 Mbps. Good 720p.
- 25 MB over 5 minutes: about 0.7 Mbps. Acceptable 720p for talking and slides.
- 25 MB over 10 minutes: about 0.3 Mbps. Expect 480p or a soft 720p.
- 50 MB over 10 minutes: about 0.7 Mbps. Good 720p.
What to do when it does not fit
Trim to the part people need, accept a lower resolution, or pick a larger size if the place you are sending to allows it. Trimming is the most effective change, because every second you remove gives the remaining seconds more data.
Screen recordings and talking-head videos stay readable at low bitrates. Fast sports and games with lots of motion need more.
Check before you commit
Drop the video into the compressor and pick the size. The quality indicator and the estimated output show whether it will look good before any work starts, so you can trim or change the size first.
Technical details
How the numbers are worked out
File size is bitrate times duration, so the average bitrate you can afford is the size in megabits divided by the seconds. About three percent is kept back for the container, and audio takes its share first, so the video gets a little less than the totals above.
The compressor compares the video bitrate with the number of pixels per second to judge quality (bits per pixel). Below a threshold it lowers the resolution, then the frame rate, rather than letting every frame turn blocky.